1. Field of the Invention
The present invention relates to a multi-tube heat exchanger, and more particularly to an improved connection structure between tubes and a pair of tanks in the heat exchanger.
2. Description of the Related Art
In a conventional multi-tube heat exchanger having a pair of tanks spaced from each other and a plurality of heat transfer tubes fluidly interconnected between the tanks, usually, tube insertion holes are provided on walls of the respective tanks facing each other and the heat transfer tubes are brazed to the tanks at a condition where the end portions of the respective tubes are inserted into respective corresponding tube insertion holes.
In such a multi-tube heat exchanger, in order to facilitate the assembly, particularly, facilitate insertion of the heat transfer tubes into the tank holes in the assembly, and in order to ensure the positional accuracy between the tubes and the tanks, radially enlarged portions or radially contracted portions are provided on both end portions of the respective tubes, and the enlarged or contracted portions are engaged to the corresponding walls of the tanks.
For example, as shown in FIG. 6, radially contracted portions 102 are formed on both end portions of each heat transfer tube 101. At the time of assembly, the respective radially contracted portions 102 are inserted into respective corresponding tube insertion holes 103a and 104a defined on tank walls 103 and 104 of tanks 105 and 106 and engaged to the tank walls 103 and 104, respectively. In such a condition, in order to improve the brazing property of the engaging portions at the time of heating and brazing, tanks 105 and 106 are fixed from both sides using a jig 107, and each heat transfer tube 101 is brazed to tank walls 103 and 104 of the tanks 105 and 106 in a stationary condition.
However, when each heat transfer tube 101 is brazed to tank walls 103 and 104 under conditions where tanks 105 and 106 are fixed from both sides by jig 107, elongation of the heat transfer tube 101 at the time of heating and brazing is suppressed or restricted by the jig 107, because generally the coefficient of thermal expansion of the jig is lower than that of the parts forming the heat exchanger, particularly, that of the heat transfer tube 101. As a result, heat transfer tube 101 may bow or deform in any direction and a desired pitch or arrangement of a plurality of heat transfer tubes 101 is not maintained.